The United States has ordered a warship to take up position off the coast of Lebanon in a show of support for the country's embattled government.
The USS Cole was attacked by al-Qaeda in 2000
The deployment of the USS Cole is being seen as a warning to Syria which - along with Iran - backs the opposition.
The Western-backed government and the opposition have repeatedly failed to agree a deal to end political impasse.
A US official quoted by news agencies said the move was "a show of support for regional stability".
"We are very concerned about the situation in Lebanon. It has dragged on very long," the unnamed senior US official told Reuters news agency.
A US defence official quoted by Reuters said the USS Cole, a guided-missile destroyer, had left Malta on Tuesday and was heading toward Lebanon.
He stressed that once in position, it would not be within visible range of Lebanon but "well over the horizon".
The news agency said the official had indicated that the destroyer could be replaced by the USS Nassau, an amphibious assault ship, which is currently heading towards the Mediterranean.
The USS Cole was attacked in the port of Aden, Yemen, in October 2000 by water-borne al-Qaeda suicide bombers. Seventeen US sailors were killed and the ship was badly damaged.
Postponed 15 times
Lebanon has not had a president since 24 November, when pro-Syrian Emile Lahoud left office. Parliament has repeatedly failed to elect a successor amid an ongoing row over candidates.
The election was postponed once again this week, and is now due to take place on 11 March. It was the 15th such delay.
There are fears that the political deadlock could lead to escalating sectarian violence.
Recent clashes between supporters of rival factions have further raised tensions and prompted several countries to advise their citizens against travelling to Lebanon.
Saudi Foreign Minister Prince Saud al-Faisal warned earlier this month that the country was "on the verge of civil war".
The setting up of an international tribunal to try the assassins of former Prime Minister Rafiq Hariri is another source of tension.
Syria is widely blamed for the February 2005 car bomb attack that killed Hariri, but Damascus has denied any involvement.
Two months after the assassination, amid US-led international pressure, Syria withdrew its troops from Lebanon, ending a 29-year occupation.